Invalid images links when using separate admin

I have a Gatsby frontend (the Netlify URL) for my Ghost blog. I have my admin configured to another domain.

Here is my issue: I login to the admin panel and upload an image in a post. When I refresh the post (inside the admin) the image link is https://lolitaontheroad.netlify.app/content/images/2021/01/MIAMI-3--finale--1.jpg hence the image is not displayed. If I go to the post on the Gatsby site, the link is the same, the image is broken.
However, if I request https://lolitaontheroad.keru.io/content/images/2021/01/MIAMI-3--finale--1.jpg, the image is valid and displayed. It’s Ghost saving the “wrong” URL inside the blog post.

This is my config.production.json relevant parts:

  "url": "https://lolitaontheroad.netlify.app/"

I tried to add

  "admin": {
    "url": "https://lolitaontheroad.keru.io/"
  }

but then my images are 404 on https://lolitaontheroad.keru.io/content/images/2021/01/MIAMI-3--finale--1.jpg.

I don’t understand what’s happening. My configuration should be exactly the same as the Gatsby demo:

  • Gatsby frontend: https://gatsby.ghost.org
  • Admin URL: https://gatsby.ghost.io

Here, the images links are valid: they point to the .io and not the .org. What’s the configuration there? Is it running the latest Ghost version?

For reference, I had this issue when I upgraded a Ghost version. I first posted on a GitHub issue but was told to post here.